Method of manufacturing cathodes of electric discharge tubes



Patented Nov. 16,1948

, Marne!) oFMANUFAoTURING cArHoDEs j or ELECTRIC DISCHARGE TUBES] V.Robert Loosjes, Eindhoven, Netherlands, assig'nor to Hartford NationalBank and, Trust Com:

- "pany, Hartford,- (;onn., as trustee No Drawing. Application February8,1947, Se-

rial No. 727,303. In Belgium November 4, 1944 Section 1, Public Law.690, August 1 v Patent expires November 4, 1964 3 Claims.

In the manufacture of cathodes for electric discharge tubes, it issometimes desirable to incorporate a method which permits of the cathodebeing manufactured outside the tube itself and of being exposed to theatmosphere for some time. This necessity particularly occurs in the caseof cathodes that are manufactured, for example by the well-knownazide-treatment as described in the Netherlandish Specification 19,215,more generally speaking in those methods, in which an alkaline earthmetal is precipitated from the vapour phase, since in such cases thereis the risk that the barium which evaporates from the azide or othercompound or mixture would become deposited not only on the cathode butalso on other areas or parts inside the tube and causes undue emissionphenomena from those areas or parts, and in certain cases even causeshort circuits. Also in the case of cathodes which are manufacturedotherwise, for example by application and dissociation of an alkalineearth carbonate, it is important to incorporate a method in which thecathode is first manufactured in a separate space, in order to avoid thegeneration of large quantities of carbonic acid in the tube which mustthen be removed.

Th object of the present invention is to provide a method ofmanufacturing a cathode of an electric discharge tube, which consists inthat an oxide cathode manufactured in any way in a separate space iscoated with a copper, silver or gold film, is then removed from thisspace and finally incorporated in the actual tube, where the protectingouter layer is then vclatilized from the cathodes by heat.

This method provides a means of keeping the cathode for any length oftime, for example in air, and in such cases it is not essential that thecathode should be manufactured inside of the tube in which it is to beused ultimately. It is desirable to use a protective layer which has nodetrimental effect during volatilisation. Thus, for example, theprotective metal films made of copper, silver or gold have advantagesover the well-known layers made of a hydrocarbon, such as parafiin,polystyrene and similar substances, because the latter substancesproduce harmful gases during volatilisation, whereas the metalsaccording to the invention practically have no detrimental effect. It isin many cases, even advantageous when a grid or an anode is coated witha copper, silver or gold film. The coating with copper, silver or goldcan be readily effected by volatilization from a Wire Which is arrangedin the proximity of the cathode. The protective film need only have athickness of some few microns.

In order that the invention may be clearly understood and readilycarried into effect, it will now be set out'more fully with reference totwo embodiments, given by way of example, in which methods according tothe invention are described in detail.

Barium-azide is heated and dissociated in a separate, exhausted space;next barium is volatilized and the vapour produced deposited on a corebody, the surface of which is constituted by nickel oxide or copperoxide; an emissive layer of barium oxide is then formed by heat. Next,the barium oxide has a protective copper film applied to it byvolatilization in the same space and the cathode, after being kept inthe air for any length of time, is incorporated in the actual tube, theprotective copper film being removed by volatilization.

In an alternative embodiment of the method according to the invention, acathode core body is coated in known manner with a layer of a mixture ofbariumand strontiumcarbonate; these carbonates are then dissociated, thecarhome acid formed is pumped off and the alkaline earth oxide left onthe core is coated with a silver film. The cathode is then removed fromthis space and after being kept in air for any length of time, isincorporated in the actual tube, the silver film being removed byvolatilization.

What I claim is:

1. A method of manufacturing a cathode of an electric discharge tube,which comprises treating a cathode core with an alkaline earth materialin an evacuated space to provide a layer of an alkaline earth metaloxide, coverin the layer with a film of a metal selected from the groupconsisting of copper, silver, and gold, removing the cathode thus formedfrom that space and disposing the cathode in the tube in which it is tobe used, sealing the tube and removing the metal film from the cathodeby volatilization of the metal.

2. A method of manufacturing a cathode of an electric discharge tube asclaimed in claim 1, including heating and dissociating an alkaline earthmetal azide in an exhausted space separate from the tube in which thecathode is to be used, depositing the alkaline earth metal vapour thusproduced on a cathode core having a surface of nickel oxide or copperoxide, and then coating this body with a metal selected from the groupconsisting of copper, silver and. gold film, then removing the cathodethus obtained from the 3 said space and housing it in the actual tubewhere it is to be used, and then volatilizing the metal film.

3. A method of manufacturing a cathode of an electric discharge tube asclaimed in claim 1, including the step of applying an alkaline earthcarbonate to a cathode core body, then heating and dissociating thecarbonate in an exhausted space separate from the tube in which theoathode is to be used, coating thealkaline earth oxide with a film ofmetal selected from the group-consisting of silver, copper and gold,removing the body thus obtained from the said space and housing it inthe actual tube, and then removing the protective metal film byvolatilization.

ROBERT LOOSJES.

REFERENCES CITED The following references-are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,936,334 Miesse Nov. 21, 19331,936,419 Asao et a1 Nov. 21, 1933 FOREIGN PATENTS Number Country Date255,090 Great Britain June 9, 1927

